Storage domains of a plurality of host computers are often stored in a single storage device. This tendency is promoted by, for example, a disk array. The disk array provides redundancy of the storage domains by a plurality of magnetic disk devices in a system, thereby increasing reliability and providing a necessary storage domain as a logical volume to a plurality of hosts. One of the merits of using this disk array is capacity expansion of the logical volume.
For example, when a computer has used up a logical volume provided by a disk array, a free space in the disk array is selected with an arbitrary length to be allocated as a logical volume, so that the computer can connect this logical volume to a logical volume in use, thereby expanding the storage domain. This function of volume expansion can also be performed on-line and is called on-line volume expansion. The on-line volume expansion enables to expand a range of the logical volume storage domain corresponding to data increasing as time passes, without stopping the application and accordingly, enables to expand the application operation time. Moreover, upon volume capacity transfer, there is no need of data transfer between volumes, which significantly reduces the storage management cost.
Conventionally, a logical volume user should report to a logical volume provider when expanding the on-line volume. In a small-size site such as within a single enterprise, there is no sudden data increase and it is not necessary to perform on-line volume expansion all the time. However, in a large-size site such as a data center where a plurality of enterprises utilize data, there is a possibility of a sudden data increase from computers of the plurality of enterprises and it is necessary to perform the on-line volume expansion more often. Moreover, in order to enhance the utilization effect of a storage domain of a disk array or the like, it is necessary to provide a volume to a plurality of users in a single storage device without waste.
In order to effectively use a storage domain in a storage device, it is necessary to manage the storage area in unit of a logical volume of a small capacity and to expand the logical volume with the small-capacity logical volume when required. When using the on-line volume expansion in this condition, there is a case that a request for the on-line volume expansion is simultaneously caused by a plurality of users and the logical volume provider may not be able to satisfy the requests. In the worst case, the on-line volume expansion cannot be performed due to lack of physical disk space in array and possibly resulting in suspension of the computer I/O operations.
Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follow.